JP7340622B2 - Cutting tools - Google Patents

Description

The present invention relates to cutting tools.

Patent Document 1 discloses a cutting tool containing titanium nitride, alumina, and yttria using silicon nitride as a matrix. It is stated that this cutting tool has the effect of increasing wear resistance by combining a silicon nitride matrix with titanium nitride, which has excellent thermal conductivity and a low coefficient of friction. . Such cutting tools are often used under harsh conditions such as high-speed machining where heat is easily generated.

Patent Document 2 discloses that in a sialon sintered body in which a Sialon phase consisting of β-Sialon and α-Sialon or a Sialon phase consisting of β-Sialon is the main phase and a sintering aid is added, Ti carbide nitride is used. A cutting tool containing one or more selected from compounds, oxides, carbonitrides, and oxynitrides is disclosed. Compared to silicon nitride, titanium compounds have lower reactivity with iron and carbon, which are the main components of the work material, so adding them to silicon nitride can suppress the reaction with the work material. It says that it can be done. Such cutting tools are often used as materials for machining super heat-resistant alloys.

Japanese Patent Application Publication No. 2000-354901 JP2005-231928A

In recent years, cutting tools are required to have high efficiency machining, and further extension of tool life is desired. In order to extend tool life, techniques to improve fracture resistance are being considered. However, in the technologies that have been studied so far, there is still room for consideration regarding fracture resistance during processing, such as wet processing, in which the temperature of the cutting edge is difficult to rise.

The present invention has been made in view of the above circumstances, and an object of the present invention is to improve fracture resistance. The present invention can be realized as the following forms.

[1] A cutting tool made of a silicon nitride sintered body containing a matrix phase made of silicon nitride or sialon, a hard phase, and a grain boundary phase in which a glass phase and a crystal phase exist,
The silicon nitride sintered body is
Containing yttrium in an oxide equivalent of 5.0 wt% or more and 15.0 wt% or less, and containing titanium nitride as the hard phase of 5.0 wt% or more and 25.0 wt% or less,
In the X-ray diffraction peak in the silicon nitride sintered body,
In an internal region deeper than 1.0 mm from the surface of the silicon nitride sintered body, a halo pattern is exhibited in a 2θ range of 25° to 35°,
Regarding the maximum peak intensity A of the matrix phase and the maximum peak intensity B of the crystalline phase present in the grain boundary phase, which are defined as follows, the ratio of the maximum peak intensity B to the maximum peak intensity A is B/A is
In the surface area up to 0.2 mm from the surface of the silicon nitride sintered body, the following formula (1) is satisfied,
The internal region of the silicon nitride sintered body satisfies the following equation (2).

0.11≦B/A≦0.40...Formula (1)
0.00≦B/A<0.10...Formula (2)

When the matrix phase consists of a single type, the maximum peak intensity A is determined as the maximum peak intensity of that phase, and when the matrix phase consists of multiple types, the maximum peak intensity A is determined as the sum of the maximum peak intensities of each of those phases. demand.
The maximum peak intensity B is determined as the maximum peak intensity of the crystal phase existing in the grain boundary phase when it consists of a single type, and the crystal phase existing in the grain boundary phase consists of multiple types. In this case, it is calculated as the sum of the maximum peak intensities of each of those phases.

[2] When observing the cross section of the silicon nitride sintered body,
In the surface region of the silicon nitride sintered body, the area ratio Cs occupied by the grain boundary phase is 7.0 area % or more and 14.0 area % or less, with the area of the entire field of view being 100 area %,
In the internal region of the silicon nitride sintered body, the area ratio Ci occupied by the grain boundary phase is 3.0 area % or more and 9.0 area % or less, with the area of the entire field of view being 100 area %,
The cutting tool according to [1], which satisfies the relationship of formula (3) below.

Cs>Ci...Formula (3)

[3] When observing the cross section of the silicon nitride sintered body,
Among all the particles of the silicon nitride or the Sialon, the proportion of particles having a maximum diameter of 0.5 μm or less is 50% or more,
Among the particles of the silicon nitride or the sialon and having a minimum diameter of 0.5 μm or more, the ratio of the number of particles having an aspect ratio of 1.5 or more is 55% or more [1] or [2] ] The cutting tool described in ].

[4] According to any one of [1] to [3], the X-ray diffraction peak in the surface region of the silicon nitride sintered body does not show a halo pattern in the range of 2θ from 25° to 35°. cutting tools.

The ceramic sintered body of the present invention has excellent fracture resistance.
In the ceramic sintered body of the present invention, when the area ratio occupied by the grain boundary phase satisfies specific requirements, the ceramic sintered body has better fracture resistance.
In the ceramic sintered body of the present invention, when the morphology of silicon nitride or sialon particles satisfies specific requirements, the ceramic sintered body has better fracture resistance.
In the ceramic sintered body of the present invention, when the surface area satisfies specific requirements, wear resistance can be improved in addition to chipping resistance.

FIG. 2 is an explanatory diagram schematically showing the state of each phase contained in a silicon nitride sintered body. FIG. 2 is a perspective view schematically showing a cutting tool. 3 is a diagram showing an X-ray diffraction pattern in an internal region of Experimental Example 1. FIG. FIG. 2 is an explanatory diagram schematically showing an X-ray diffraction pattern when the crystal phases existing in the grain boundary phase are composed of a plurality of types. 3 is a diagram showing an X-ray diffraction pattern in the surface region of Experimental Example 1. FIG.

The present invention will be explained in detail below. In this specification, descriptions using "~" for numerical ranges include the lower limit and upper limit unless otherwise specified. For example, the description "10 to 20" includes both the lower limit value of "10" and the upper limit value of "20". That is, "10 to 20" has the same meaning as "10 or more and 20 or less".

1. cutting tool 1
The cutting tool 1 is made of silicon nitride containing a matrix phase 3 made of silicon nitride (Si ₃ N ₄ ) or sialon (SiAlON), a hard phase 4 , and a grain boundary phase 10 in which a glass phase 11 and a crystalline phase 12 are present. It consists of a quality sintered body 2.
The silicon nitride sintered body 2 contains 5.0 wt% or more of yttrium and 15.0 wt% or less in terms of oxide, and also contains titanium nitride as the hard phase 4 of 5.0 wt% or more and 25.0 wt% or less. In the silicon nitride sintered body 2, in the X-ray diffraction peak of the silicon nitride sintered body 2, 2θ is from 25° to 35° in an internal region deeper than 1.0 mm from the surface of the silicon nitride sintered body 2. A halo pattern is shown in the range of . The silicon nitride sintered body 2 has the maximum peak intensity A of the matrix phase 3 and the maximum peak intensity B of the crystal phase 12 present in the grain boundary phase 10 defined as follows. B/A, which is the ratio of peak intensity B, satisfies the relationship of the following formula (1) in the surface area up to 0.2 mm from the surface of the silicon nitride sintered body 2, and the above relationship of the silicon nitride sintered body 2 is satisfied. In the internal region, the following equation (2) is satisfied.

0.11≦B/A≦0.40...Formula (1)
0.00≦B/A<0.10...Formula (2)

If the matrix phase 3 consists of a single type, the maximum peak intensity A is determined as the maximum peak intensity of that phase, and if the matrix phase 3 consists of multiple types, the maximum peak intensity A is determined as the sum of the maximum peak intensities of each of those phases. demand.
When the crystal phase 12 present in the grain boundary phase 10 consists of a single type, the maximum peak intensity B is determined as the maximum peak intensity of that phase, and the crystal phase 12 present in the grain boundary phase 10 consists of multiple types. In this case, it is calculated as the sum of the maximum peak intensities of each of those phases.

2. Silicon nitride sintered body 2
(1) Phase structure of the silicon nitride sintered body 2 As schematically shown in FIG. 1, the silicon nitride sintered body 2 has a grain boundary phase 10 between the matrix phase 3 and the hard phase 4. . Matrix phase 3 consists of silicon nitride or sialon. This silicon nitride or sialon may be in any of α phase, β phase, polytype, and composite phases thereof. The grain boundary phase 10 includes a glass phase 11 and a crystalline phase 12. Note that FIG. 1 conceptually shows each phase, and does not accurately show the shape and size of each phase.

(2) Components contained in the silicon nitride sintered body 2 and the content of each component The content of yttrium is 5.0 wt% or more in terms of oxide, from the viewpoint of obtaining a densified sintered body. . From the viewpoint of suppressing the amount of crystalline phase 12 in grain boundary phase 10, the content of yttrium is 15.0 wt% or less in terms of oxide. Therefore, the content of yttrium is 5.0 wt% or more and 15.0 wt% or less in terms of oxide.

The content of titanium nitride as the hard phase 4 is 5.0 wt% or more from the viewpoint of providing sufficient wear resistance and improving the chemical reaction resistance of the silicon nitride sintered body 2. The reason why the chemical reaction resistance of the silicon nitride sintered body 2 is improved is that titanium nitride has a lower reactivity with the work material than silicon nitride or sialon that constitutes the matrix phase 3. The content of titanium nitride as the hard phase 4 is 25.0 wt% or less from the viewpoint of promoting the growth of particles constituting the matrix phase 3. Therefore, the content of titanium nitride as the hard phase 4 is 5.0 wt% or more and 25.0 wt% or less in terms of oxide.

The content (wt%) of each component can be determined as the amount of each component when the weight of the silicon nitride sintered body 2 is 100 wt%.
The content of other components in the silicon nitride sintered body 2 is not particularly limited. The silicon nitride sintered body 2 may contain 3.0 wt% or more and 10.0 wt% or less of aluminum in terms of oxide. When the aluminum content is 3.0 wt% or more in terms of oxide, reactivity with the work material can be suppressed. When the aluminum content is 10.0 wt % or less in terms of oxide, the strength of the matrix phase does not decrease and the wear resistance can be improved.
When the silicon nitride sintered body 2 consists of silicon nitride or sialon, yttria (Y ₂ O ₃ ), alumina (Al ₂ O ₃ ), titanium nitride (TiN), and inevitable impurities, silicon nitride or sialon is used. The content of is the remainder of the total (wt%) of titanium nitride, alumina, yttria, and unavoidable impurities. The content of unavoidable impurities can be 0.1 wt% or less.

(3) Requirements regarding the halo pattern in the internal region In the internal region deeper than 1.0 mm from the surface of the silicon nitride sintered body 2, the silicon nitride sintered body 2 has a halo in the range of 2θ from 25° to 35°. Show a pattern. According to this configuration, fracture resistance can be significantly improved. The reason for this is not certain, but the probable reason will be explained later.

The presence or absence of this halo pattern is determined by whether or not the X-ray diffraction pattern has a pattern having a broad 2θ range of 25° to 35°. Specifically, as shown in FIG. 3, when 2θ is 25°, the line segment PQ connecting the point P with the lowest intensity when 2θ is 20° or less and the point Q with the lowest intensity when 2θ is 40° or more It is determined that a halo pattern is present when the minimum value of the X-ray diffraction intensity in the range from 35° to 35° is higher. That is, the presence or absence of a halo pattern is determined by whether or not there is a broad pattern that exhibits a higher intensity than line segment PQ, which is a virtual baseline, in the range of 2θ from 25° to 35°. The presence of such a halo pattern can be an indicator that the glass phase 11 is present in the grain boundary phase 10 in the internal region of the silicon nitride sintered body 2.

The highest intensity value of the halo pattern is preferably larger than the peak intensity value at which the standard diffraction intensity of the (h, k, l) plane in the reference JCPDS card of matrix phase 3 is 1.0. This will be specifically explained with reference to FIG. 3. As shown in Figure 3, the highest intensity value of the halo pattern is the intensity of the highest intensity part of the X-ray diffraction curve, excluding the peak of the crystalline phase, and is observed at around 2θ of 30°. . The peak at which the standard diffraction intensity of matrix phase 3 is 1.0, which is used as a reference, is seen around 2θ of 65°, which _is indicated by the arrow in _FIG . This is the peak of the (102) plane in #00-033-1160. Comparing these intensities, the highest intensity value of the halo pattern seen around 2θ of 30° is greater than the peak intensity of the (102) plane of the silicon nitride β phase (β-Si ₃ N ₄ ). If there are multiple crystal phase peaks in the peak intensity of the (102) plane, refer to the peak intensity of other standard diffraction intensities of 1.0, such as the (420) plane and (112) plane. Bye.

Note that the cutting tool 1 that satisfies the requirements regarding the halo pattern in the internal region can be obtained by controlling the blending amount of the material forming the grain boundary phase 10, the firing conditions during the production of the silicon nitride sintered body 2, etc. can.

(4) Requirements regarding the maximum peak intensity ratio of the crystal phase 12 present in the matrix phase 3 and the grain boundary phase 10 The silicon nitride sintered body 2 has a ratio of the maximum peak intensity A of the crystal phase 12 present in the matrix phase 3 to the The ratio B/A of the maximum peak intensity B of the phase 12 satisfies the relationship 0.11≦B/A≦0.40 in the above surface region, and 0.11≦B/A≦0.40 in the above internal region of the silicon nitride sintered body 2. The relationship 00≦B/A<0.10 is satisfied. According to this configuration, the chipping resistance of the silicon nitride sintered body 2 can be improved while ensuring the wear resistance of the silicon nitride sintered body 2. The reason for this is not certain, but the probable reason will be explained later.

B/A, which is the ratio of maximum peak intensity B to maximum peak intensity A, is determined as follows. When the matrix phase 3 is composed of one type of silicon nitride β phase indicated by a circle as in the X-ray diffraction pattern shown in FIG. 3, the maximum peak intensity A is determined as the maximum peak intensity of that phase. In the X-ray diffraction pattern shown in FIG. 3, the peak located between 25° and 30° in 2θ is the maximum peak of the silicon nitride β phase, and the intensity of this peak is specified as the maximum peak intensity A. Examples of the matrix phase 3 include silicon nitride α phase, silicon nitride β phase, sialon α phase, sialon β phase, polytype 12H, polytype 21R, and polytype 15R. In these matrix phase 3, the JCPDS card to be referred to and the crystal plane showing the maximum peak adopted in principle are as follows. For the silicon nitride α phase, refer to JCPDS card: #00-009-0250, and in principle, the peak intensity of the (210) plane is adopted as the maximum peak intensity. For the silicon nitride β phase, refer to JCPDS card: #00-033-1160, and in principle, the peak intensity of the (200) plane is adopted as the maximum peak intensity. For the Sialon α phase, refer to JCPDS card: #00-042-0251, and in principle, the peak intensity of the (102) plane is adopted as the maximum peak intensity. For the Sialon β phase, refer to JCPDS card: #00-048-1615, and in principle, the peak intensity of the (200) plane is adopted as the maximum peak intensity. For polytype 12H, refer to JCPDS card: #00-042-0161, and in principle, the peak intensity of the (110) plane is adopted as the maximum peak intensity. For polytype 21R, refer to JCPDS card: #00-053-1012, and in principle, the peak intensity of the (101) plane is adopted as the maximum peak intensity. For polytype 15R, refer to JCPDS card: #00-042-0160, and in principle, the peak intensity of the (101) plane is adopted as the maximum peak intensity.

In addition, if the maximum peak value of the reference crystal phase overlaps with the peak of another crystal phase, select the peak value with the highest intensity that does not overlap, and perform the standard diffraction of the (h, k, l) plane corresponding to that peak. From the intensity, each peak intensity ratio is calculated using the theoretical intensity value as the maximum peak intensity. Specifically, when the selected peak intensity is I and the standard diffraction intensity of the (h, k, l) plane corresponding to the peak is Io, the reference value X is expressed by the following formula.
X=I/Io*100

As in the X-ray diffraction pattern of FIG. 3, when the crystalline phase 12 present in the grain boundary phase 10 is composed of one type of other crystalline phases indicated by square marks, the maximum peak intensity B is the maximum peak of that phase. Obtained as strength. In FIG. 3, the peak located between 30° and 35° in 2θ is the maximum peak of the crystalline phase 12 present in the grain boundary phase 10, and the intensity of this peak is specified as the maximum peak intensity B. _The crystal _phases 12 existing in the grain _boundary phase 10 include _Y2SiAlO5N , _{Y4SiAlO8N , Y3AlSi2O7N2} , _Y10 ( _{Si6O22N2 ) O2 , YSiO2N .} can be exemplified. In these crystal phases 12, the JCPDS card to be referred to and the crystal plane showing the maximum peak adopted in principle are as follows. For Y ₂ SiAlO ₅ N, refer to JCPDS card: #00-048-1627, and in principle, the peak intensity of the (102) plane is adopted as the maximum peak intensity. For Y ₄ SiAlO ₈ N, refer to JCPDS card: #00-048-1630, and in principle, the peak intensity of the (201) plane is adopted as the maximum peak intensity. For Y ₃ AlSi ₂ O ₇ N ₂ , refer to JCPDS card: #00-043-0579, and in principle, the peak intensity of the (100) plane is adopted as the maximum peak intensity. For Y ₁₀ (Si ₆ O ₂₂ N ₂ ) O ₂ , refer to JCPDS card: #01-083-6656, and in principle, the peak intensity of the (211) plane is adopted as the maximum peak intensity. For YSiO ₂ N, refer to JCPDS card: #00-048-1624, and in principle, the peak intensity of the (20-4) plane is adopted as the maximum peak intensity. Note that in the Miller index, a direction having a negative component is usually written with a bar above the number, but in this specification, for convenience, it is written in parallel with the number. For example, as described above, it is written as "(20-4)". In this case, the third "-4" has the same meaning as a "bar" added above "4".

When the crystal phases 12 present in the grain boundary phase 10 are composed of a plurality of types, the maximum peak intensity B is determined as the sum of the maximum peak intensities of each of the phases. How to obtain this will be explained with reference to FIG. 4. In FIG. 4, square marks indicate the first polycrystalline phase, square prime marks indicate a second polycrystalline phase that is different from the first polycrystalline phase, and square double prime marks represent the first polycrystalline phase. A third polycrystalline phase that is a different crystal phase from the other crystalline phases and the second polycrystalline phase is shown. The peak marked with "max" in each mark in FIG. 4 is the maximum peak of that phase. For example, in FIG. 4, two peaks of the second polycrystalline phase marked with square prime marks are recognized, and the peak on the left, which has the highest intensity, is the maximum peak of the second polycrystalline phase. In such an X-ray diffraction pattern, the maximum peak intensity B is the maximum peak intensity of the first other crystal phase marked with a square max and the maximum peak of the second other crystal phase marked with a square prime max. It is determined as the sum of the intensity and the maximum peak intensity of the third other crystal phase to which the square double prime max is attached.

Similarly to the case where the crystalline phase 12 existing in the grain boundary phase 10 consists of a plurality of types, when the matrix phase 3 consists of a plurality of types, the maximum peak intensity A is the sum of the maximum peak intensities of each of those phases. Find it as.

Note that the cutting tool 1 that satisfies the requirements regarding the maximum peak intensity ratio of the crystal phase 12 existing in the matrix phase 3 and the grain boundary phase 10 is based on the amount of the material forming the grain boundary phase 10, the silicon nitride sintered body 2 This can be obtained by controlling the firing conditions during manufacturing.

(5) Requirements regarding the ratio of the area occupied by the grain boundary phase 10 When the cutting tool 1 observes the cross section of the silicon nitride sintered body 2, in the above surface area of the silicon nitride sintered body 2, the entire visual field is When the area is 100 area%, the area ratio Cs occupied by the grain boundary phase 10 is 7.0 area% or more and 14.0 area% or less, and in the internal region of the silicon nitride sintered body 2, the area of the entire visual field is It is preferable that the area ratio Ci occupied by the grain boundary phase 10 is 3.0 area % or more and 9.0 area % or less, and satisfies the relationship of the following formula (3), where is 100 area %.

Cs>Ci...Formula (3)

The area ratios Cs and Ci occupied by the grain boundary phase 10 are determined as follows. A cross section passing through both the surface region and the internal region of the silicon nitride sintered body 2 was observed using a SEM (scanning transmission electron microscope), and each of the surface region and the internal region of the silicon nitride sintered body 2 was observed. A SEM image of an area of 24 μm×18 μm is obtained. By binarizing the SEM image using image processing software WinrROOF, the grain boundary phase 10 existing between the matrix phase 3 and the hard phase 4 is identified, and the area of the grain boundary phase 10 is calculated. Then, the ratios Cs and Ci of the area occupied by the grain boundary phase 10 to the area of the entire visual field are determined.
In addition, a plurality of SEM images in a range of 24 μm x 18 μm were observed for each of the surface area and the internal area of the silicon nitride sintered body 2, and at least one set of the SEM images satisfied the above requirements. That's fine.

The area ratio Cs occupied by the grain boundary phase 10 is preferably 7.0 area % or more from the viewpoint of improving grain boundary strength. Further, the area ratio Cs occupied by the grain boundary phase 10 is preferably 14.0 area % or less from the viewpoint of maintaining wear resistance. Therefore, the area ratio Cs occupied by the grain boundary phase 10 is preferably 7.0 area % or more and 14.0 area % or less.

The area ratio Ci occupied by the grain boundary phase 10 is preferably 3.0 area % or more from the viewpoint of maintaining the strength of the silicon nitride sintered body 2. Further, the area ratio Ci occupied by the grain boundary phase 10 is preferably 9.0 area % or less from the viewpoint of promoting the growth of particles constituting the matrix phase 3. Therefore, the area ratio Ci occupied by the grain boundary phase 10 is preferably 3.0 area % or more and 9.0 area % or less.

(6) Requirements regarding the morphology of silicon nitride or sialon particles The cutting tool 1 has a maximum diameter of 0.5 μm or less among all silicon nitride or sialon particles when the cross section of the silicon nitride sintered body 2 is observed. The percentage of particles with an aspect ratio of 1.5 or more is 50% or more, and among the particles of silicon nitride or sialon with a minimum diameter of 0.5 μm or more, the percentage of particles with an aspect ratio of 1.5 or more is preferably 55% or more.

The maximum diameter and aspect ratio of silicon nitride or sialon particles are determined as follows. A cross section passing through the internal region of the silicon nitride sintered body 2 is observed using a SEM, and a SEM image of the internal region of the silicon nitride sintered body 2 in a range of 24 μm×18 μm is obtained. By subjecting this SEM image to image analysis processing, the maximum diameter X and minimum diameter Y of each silicon nitride or sialon particle are determined. Then, the aspect ratio (X/Y) of each silicon nitride or sialon particle is calculated.
Note that it is only necessary to observe a plurality of SEM images of the silicon nitride sintered body 2 in a range of 24 μm×18 μm, and the above requirements are satisfied in at least one of the SEM images.

The ratio of the number of particles having a maximum diameter of 0.5 μm or less among all silicon nitride or sialon particles is preferably 50% or more from the viewpoint of atomization and homogenization of the particles constituting the matrix phase 3. Among silicon nitride or sialon particles with a minimum diameter of 0.5 μm or more, the proportion of particles with an aspect ratio of 1.5 or more produces a so-called diffraction effect that curves the generated crack. From this viewpoint, it is preferably 55% or more, and more preferably 60% or more.

(7) Requirements regarding the halo pattern in the surface region The silicon nitride sintered body 2 preferably does not exhibit a halo pattern in the 2θ range of 25° to 35° in the surface region up to 0.2 mm from the surface.

Note that the cutting tool 1 that satisfies the requirements regarding the halo pattern in the surface region can be obtained by controlling the blending amount of the material forming the grain boundary phase 10, the firing conditions during the production of the silicon nitride sintered body 2, etc. can. Although the detailed reason is not clear, the larger the amount of WC contained in the silicon nitride sintered body 2, the more easily the surface area of the silicon nitride sintered body 2 is sintered, and the amount of crystalline phase in the grain boundary phase increases. There is a tendency to

3. Method for manufacturing silicon nitride sintered body 2 The method for manufacturing silicon nitride sintered body 2 is not particularly limited. An example of a method for manufacturing the silicon nitride sintered body 2 is shown below.

(1) Raw materials The following raw material powders are used as raw materials.
・Silicon nitride powder ( _{Si3N4 powder} )
・Aluminum oxide powder ( _{Al2O3 powder} )
・Yttrium oxide powder ( _{Y2O3 powder} )
・Titanium nitride powder (TiN powder)

(2) Preparation of powder for firing The above-mentioned powders are weighed so as to have a predetermined mixing ratio. The weighed powder is placed in a ball mill, and mixed and ground with alcohol (for example, ethanol) and grinding media. The obtained slurry is dried in a hot water bath to obtain a dry mixed powder.

(3) Press molding The obtained mixed powder is press molded. The molded body obtained by press molding is molded by cold isostatic pressing (CIP).

(4) Firing The compact obtained by cold isopressing is heated at a predetermined temperature in a nitrogen atmosphere set to reduced pressure to perform a degreasing treatment. The degreased molded body is heated at a predetermined temperature in a nitrogen atmosphere to perform a firing treatment. The firing process has two temperature raising conditions: a first temperature increase and a second temperature increase performed subsequent to the first temperature increase. It is preferable that the temperature increase rate of the second temperature increase is faster than that of the first temperature increase. Moreover, it is preferable that the atmospheric pressure in the second temperature increase is higher than that in the first temperature increase. After the second temperature increase, the increased temperature is maintained for a predetermined period of time. Then, a cooling treatment is performed at a predetermined temperature decreasing rate, and a silicon nitride sintered body is obtained.

In the sintering process, the vicinity of the surface of the molded body tends to be more easily sintered than the inside. Therefore, by providing a first temperature increase and a second temperature increase in the sintering process, the requirements regarding the halo pattern and the maximum peak intensity ratio of the crystal phase 12 present in the matrix phase 3 and the grain boundary phase 10 are satisfied. A silicon nitride sintered body 2 can be suitably obtained. That is, during the second temperature rise, which is a high temperature range where sintering progresses (e.g., 1650°C or higher), the silicon nitride sintering rate is increased compared to the first temperature rise, which is a low temperature range (e.g., 1400°C or lower). The ratio of the glass phase 11 and the crystalline phase 12 in the grain boundary phase 10 can be controlled in the internal region and the surface region of the compact 2. The second temperature increase is preferably carried out under pressurized conditions of, for example, 0.15 MPa to 0.40 MPa. Sufficient sinterability can be obtained if the pressure conditions for the second temperature increase are 0.15 MPa or higher. Further, if the pressure conditions for the second temperature increase are 0.40 MPa or less, the amount of grain boundary phase in the silicon nitride sintered body 2 is ensured, especially in the vicinity of the surface, and the silicon nitride sintered body 2 is Able to maintain strength.

4. Other configurations of cutting tool 1 The shape of cutting tool 1 is not particularly limited. For example, the silicon nitride sintered body 2 can be shaped and surface-finished by at least one of cutting, grinding, and polishing to form the cutting tool 1 (see FIG. 2). Of course, the silicon nitride sintered body 2 may be used as it is as the cutting tool 1.

The cutting tool 1 has a silicon nitride sintered body 2 as a base material, and the surface of the base material is coated with carbides, nitrides, oxides, carbonitrides, carbonates, nitrides, and oxides of titanium, chromium, and aluminum. A surface coating layer made of at least one compound selected from carbonitoxides may be formed.
When the surface coating layer is formed, the surface hardness of the cutting tool 1 increases, and the progression of wear due to reaction and welding with the workpiece is suppressed. As a result, the wear resistance of the cutting tool 1 is improved.
The at least one compound selected from carbides, nitrides, oxides, carbonitrides, carbonates, nitrides, and carbonitoxides of titanium, chromium, and aluminum includes, but is not particularly limited to, TiN, Suitable examples include TiAlN, TiAlCrN, and AlCrN.
The thickness of the surface coating layer is not particularly limited. The thickness of the surface coating layer is preferably 0.02 μm or more and 30 μm or less from the viewpoint of wear resistance.

5. Estimated Reason for Superior Fracture Resistance Here, the presumed reason why the cutting tool 1 of the present disclosure is superior in fracture resistance will be explained.
The silicon nitride sintered body 2 has sinterability by containing 5.0 wt% or more of yttrium in terms of oxide. In addition, the silicon nitride sintered body 2 contained 15.0 wt % or less of yttrium in terms of oxide, thereby suppressing the amount of the crystal phase 12 in the grain boundary phase 10 to a predetermined amount or less.
By containing 5.0 wt% or more of titanium nitride as the hard phase 4, the silicon nitride sintered body 2 has improved sinterability and can reduce internal pores. Furthermore, by containing this titanium nitride in an amount of 5.0 wt% or more, the chemical reaction resistance of the silicon nitride sintered body 2 is improved. Furthermore, by containing 25 wt% or less of titanium nitride as the hard phase 4, the silicon nitride sintered body 2 makes it difficult for the growth of the particles forming the matrix phase 3 to be inhibited by the titanium nitride particles. particles can grow into needle-like shapes.
Furthermore, the silicon nitride sintered body 2 has a glass phase 11 and a crystalline phase 12 in the grain boundary phase 10, and as described above, the amount of the crystalline phase 12 in the grain boundary phase 10 with respect to the matrix phase 3 is reduced in the surface area. It is thought that the growth of thermal cracks that occurred on the surface during cutting could be suppressed by controlling the inner and outer regions. It is presumed that the effect of improving grain boundary strength due to the presence of a predetermined amount of glass phase 11 in the internal region of silicon nitride sintered body 2 contributes to this. Next, we will consider the effects of heat during cutting. The surface region of the silicon nitride sintered body 2 tends to reach a high temperature due to the heat generated by the contact between the workpiece and the cutting tool 1 . Therefore, the surface region of the silicon nitride sintered body 2 contains a large amount of the crystalline phase 12 having excellent high-temperature strength even in the grain boundary phase 10, so that wear resistance and chipping resistance are easily ensured. On the other hand, the internal region of the silicon nitride sintered body 2 is less likely to reach a high temperature than the surface region. This is noticeable in machining that does not generate much heat, such as wet rough machining of heat-resistant alloys. Therefore, it is presumed that the internal region of the silicon nitride sintered body 2 can contribute to improving the fracture resistance by including a large amount of the glass phase 11, which has superior room-temperature to medium-temperature strength, in the grain boundary phase 10. In this way, the cutting tool 1 of the present embodiment has more glass phase 11 present in the grain boundary phase 10 in the internal region than in the surface region of the silicon nitride sintered body 2, thereby ensuring wear resistance. It also has excellent fracture resistance. The cutting tool 1 made of such a silicon nitride sintered body 2 can have a long life.

When the above-mentioned requirements regarding the ratio of the area occupied by the grain boundary phase 10 are satisfied, it is presumed that the fracture resistance is improved in the following manner.
Since the surface area of the silicon nitride sintered body 2 has a large amount of the crystalline phase 12 having excellent thermal properties in the grain boundary phase 10, wear resistance is maintained by setting the area ratio Cs of the grain boundary phase 10 to an appropriate amount. can. At this time, if the area ratio Cs of the grain boundary phase 10 is 7.0 area % or more and 14 area % or less, the grain boundary strength is maintained, so that both wear resistance and chipping resistance can be achieved. On the other hand, since the internal region of the silicon nitride sintered body 2 contains the glass phase 11 having excellent strength at room to medium temperatures in the grain boundary phase 10, even if the area ratio Ci of the grain boundary phase 10 is smaller than that of the surface region. It is assumed that sudden loss is unlikely to occur. Further, the area ratio Ci occupied by the grain boundary phase 10 is smaller than the area ratio Cs occupied by the grain boundary phase 10, that is, the particles constituting the matrix phase 3 are smaller in the inner region of the silicon nitride sintered body 2 than in the surface region. By increasing the ratio, thermal cracks generated on the surface of the silicon nitride sintered body 2 are suppressed from propagating inside. At this time, if the area ratio Ci of the grain boundary phase 10 is 3.0 area % or more and 9.0 area % or less, the strength of the silicon nitride sintered body 2 is maintained and the particles constituting the matrix phase 3 are Growth is sufficiently promoted.

When the above-mentioned requirements regarding the aspect ratio of silicon nitride or sialon particles are satisfied, it is presumed that the fracture resistance is improved in the following manner. By setting the ratio of particles with a maximum diameter of 0.5 μm or less to 50% or more of all the particles of silicon nitride or Sialon, the particles constituting the matrix phase 3 can be made fine and homogeneous, and the particles between the fine particles can be made fine and homogeneous. Strength is increased by reducing bond size. Further, when the proportion of particles having a minimum diameter of 0.5 μm or more and an aspect ratio of 1.5 or more is 55% or more, the so-called diffraction effect that curves cracks generated in the silicon nitride sintered body 2 becomes large.

When the above-mentioned requirements regarding the halo pattern in the surface area are satisfied, it is presumed that the wear resistance is improved in the following manner. Since the X-ray diffraction peak in the surface region of the silicon nitride sintered body 2 does not show a halo pattern in the range of 2θ from 25° to 35°, the grain boundary phase is not observed in the surface region of the silicon nitride sintered body 2. No. 10 does not contain a glass phase that easily softens at high temperatures. Therefore, the wear resistance of the silicon nitride sintered body 2 is further improved, and damage in the surface region is less likely to occur or damage that has occurred is less likely to progress. The cutting tool 1 made of such a silicon nitride sintered body 2 can have a long life.

In this way, in this embodiment, the grain boundary phase 10 in the surface region of the cutting tool 1 is crystallized, and a predetermined amount of the glass phase 11 is present in the internal region, thereby reducing the temperature at the cutting edge of the cutting tool 1, which is at the highest temperature. It is presumed that the strength in the internal region was improved while maintaining wear resistance and chipping resistance. In particular, it is expected to have the effect of extending tool life by suppressing defects such as flaking in machining that does not reach very high temperatures during cutting, such as wet rough machining when machining super heat-resistant alloys.

In the following experiments, each of the silicon nitride sintered bodies of Experimental Examples 1 to 21 was produced, and each of these silicon nitride sintered bodies was processed to obtain Experimental Examples 1 to 21 cutting tools. Experimental Examples 1 to 12 are Examples, and Experimental Examples 13 to 21 are Comparative Examples.

1. Preparation of Ceramic Sintered Body (1) Mixing Table 1 shows the formulation of the raw material powders used in the ceramic sintered bodies of each Example and Comparative Example.
In addition, the raw material powder is shown below.
Si ₃ N ₄ powder: Average particle size 1.0 μm or less Y ₂ O ₃ powder: Average particle size 3.0 μm
_{Al2O3 powder} : average particle size 0.4μm
TiN powder: average particle size 0.5 μm to 2.0 μm
However, the TiN powder contains about 0.1 to 2.0 wt% of WC (tungsten carbide). If the total mass of the above four types of powder is 100.0 wt%, the content of WC is less than 0.1 wt%. Therefore, in Table 1, the blending ratios of the four types of powders are listed assuming that the WC content is 0.

(2) Mixing The powder obtained with the above formulation was placed in a ball mill having an inner wall made of silicon nitride, and mixed with ethanol and grinding media. A silicon nitride-based coccule with a diameter of 6 to 10 mm was used as the grinding media, and the mixture was ground and mixed for about 72 hours to prepare a mixture (slurry).

(3) Drying and Granulation The resulting mixture to which 3.5 wt % of organic binder was added was dried in hot water and passed through a 250 μm sieve to obtain a mixed powder.
Note that the steps up to this point are common to the silicon nitride sintered bodies of all Examples and Comparative Examples.

(4) Press molding The mixed powder obtained through the above steps was press molded at a pressure of 1000 kgf/cm ² . The obtained molded body was molded by CIP molding at a pressure of 1500 kgf/cm ² .

(5) Firing (5-1) Silicon nitride sintered bodies of Experimental Examples 1 to 12 The silicon nitride sintered bodies of Experimental Examples 1 to 12 were fired in the following manner to obtain silicon nitride sintered bodies. Ta.
The molded body obtained above was degreased at 800° C. for 30 minutes in a nitrogen atmosphere set at reduced pressure. In the degreasing treatment, the temperature increase rate was 1.5°C/min to 3.0°C/min, and in the process of increasing the temperature to 800°C, the temperature was held in steps of 100°C to 200°C for 30 minutes or more. The degreased molded body was fired in a silicon nitride container. Specifically, the first temperature increase was performed from 1200 °C to 1400 °C at a temperature increase rate of 5 °C/min to 10 °C/min and a nitrogen atmosphere of 0.01 MPa to 0.10 MPa. A second temperature increase was performed from 1650° C. to 1850° C. at a rate of 10° C./min to 20° C./min and a nitrogen atmosphere of 0.15 MPa to 0.40 MPa. Thereafter, holding was performed for 3 to 6 hours. After holding for a predetermined time, cooling treatment was performed at a temperature decreasing rate of 10° C./min to 20° C./min to obtain a silicon nitride sintered body.
(5-2) Silicon nitride sintered bodies of Experimental Examples 13 to 21 The silicon nitride sintered bodies of Experimental Examples 13 to 21 were fired at a heating rate of 5°C/min to 10°C/min in a nitrogen atmosphere of 0.5°C. The temperature is raised to 1200 °C to 1400 °C at 01 MPa to 0.10 MPa, and then the temperature is raised to 1650 °C to 1850 °C in a nitrogen atmosphere of 0.10 to 0.15 MPa while maintaining the temperature increase rate. were obtained in the same manner as the silicon nitride sintered bodies of Experimental Examples 1 to 11.

(6) Polishing The surface of the obtained silicon nitride sintered body was polished to obtain the final tool shape to obtain a cutting tool.

2. Analysis (1) X-ray diffraction analysis The obtained silicon nitride sintered body was polished to create polished surfaces in the surface region and internal region, and X-ray diffraction measurements were performed on each polished surface. Ta. Using CuKα rays as an X-ray source, measurements were carried out in a 2θ range of 10° to 80° under conditions of an output of 45 kV and 200 mA. The obtained X-ray diffraction peak was used to identify the crystal phase and determine the presence or absence of the above-mentioned halo pattern. The type of crystal phase was identified by comparing the X-ray diffraction peak with known crystal phases. The maximum peak intensity ratio B/A of the crystal phases present in the matrix phase and the grain boundary phase described above was calculated from the maximum peak intensity of each identified crystal phase. In addition, in Experimental Example 13, sintering was defective, and X-ray diffraction analysis was not performed. The X-ray diffraction pattern in the internal region of Experimental Example 1 is shown in FIG. 3, and the X-ray diffraction pattern in the surface region is shown in FIG. In FIGS. 3 and 5, the horizontal axis is the rotation angle (2θ), and the vertical axis is the square root of the X-ray diffraction intensity.
The presence or absence of a halo pattern in the internal region of each experimental example is shown in the "Hello pattern in internal region" column of Table 1. The maximum peak intensity ratio B/A of the crystalline phase existing in the matrix phase and the grain boundary phase in each experimental example is shown in the "X-ray intensity ratio (B/A)" column of Table 1. In the "X-ray intensity ratio (B/A)" column, the "surface" column indicates the intensity ratio of the surface area, and the "interior" column indicates the intensity ratio of the internal area. The presence or absence of a halo pattern in the surface region in each experimental example is shown in the "Hello pattern in surface region" column of Table 1.

(2) SEM Observation Further, a cross section passing through both the surface region and the internal region of the silicon nitride sintered body was mirror-finished, and after etching, the structure was observed using a scanning electron microscope. By the method described in the above-described embodiment, the area ratios Cs and Ci occupied by the grain boundary phase were calculated, and the morphology of silicon nitride or sialon particles was evaluated. In addition, in Experimental Example 13, sintering was defective, and SEM observation was not performed.
The area ratios Cs and Ci occupied by the grain boundary phase in each experimental example are shown in the "grain boundary phase amount (area %)" column of Table 1. In the "Grain boundary phase amount (area %)" column, the "Surface" column indicates the area ratio Cs occupied by the grain boundary phase in the surface region, and the "Interior" column indicates the area occupied by the grain boundary phase in the internal region. shows the ratio Ci.
The morphology of silicon nitride or sialon particles in each experimental example is shown in the "Silicon nitride particle morphology" column of Table 1. In the "Silicon nitride particle form" column, the "Percentage of maximum diameter 0.5 μm or less" column indicates the percentage of particles with a maximum diameter of 0.5 μm or less among all silicon nitride or sialon particles. The column "Ratio of minimum diameter of 0.5 μm or more and aspect ratio of 1.5 or more" indicates the proportion of silicon nitride or sialon particles with an aspect ratio of 1.5 or more among particles with a minimum diameter of 0.5 μm or more. Shows the percentage of numbers.

3. Fabrication of cutting tool The silicon nitride sintered bodies of Experimental Examples 1 to 12 and 14 to 21 were processed into a tool shape (RCGX120700T01020). In addition, in Experimental Example 13, sintering was defective, and a cutting tool was not manufactured.
Table 1 shows the composition (mixture) of the raw material powder for silicon nitride sintered bodies as described above, but since this composition does not change even after firing, the composition of each ceramic sintered body and are equivalent. Since each silicon nitride sintered body after firing is machined into a cutting tool, the composition of the raw material powder is ultimately the same as the composition of the cutting tool.

4. Cutting test (1) Test method A cutting test was conducted using each cutting tool. The test conditions are as follows.
Processing method: Turning Work material: Inconel 718 Dimensions φ150mm x 300mm
Cutting speed: 280m/min Feed rate: 0.27mm/rev
Depth of cut: 2.0mm
Cutting conditions: Wet processing Evaluation: Machining of 5.0 mm in the direction of the end surface of the outer diameter was performed twice in succession, which was considered as one cycle, and a cutting test was performed with the upper limit of 10 cycles. When the amount of damage to the tool cutting edge exceeded 0.8 mm, evaluation was made based on the number of cycles that could be processed until the amount of damage to the tool cutting edge reached 0.8 mm. In addition, when a breakage occurred before the amount of damage to the tool cutting edge reached 0.8 mm, evaluation was made based on the number of cycles until the breakage occurred.
Table 1 shows the number of cuts, amount of damage, and state of the cutting edge under the above processing conditions.

(2) Test results The test results are shown in Table 1. The amount of damage to the cutting tools of Experimental Examples 1 to 12 was less than 0.8 mm (more specifically, 0.71 mm or less) even after the upper limit of 10 cycles. On the other hand, in Experimental Example 14, chipping occurred in the 8th cycle, and the amount of damage was 0.8 mm or more. In Experimental Examples 15 to 19 and 21, flaking occurred in the 5th and 6th cycles, respectively, and the amount of damage was 0.8 mm or more. In Experimental Example 20, there was a large damage at the 7th cycle, and the amount of damage could not be measured. From these results, it was found that the cutting tools of Experimental Examples 1 to 12 had excellent fracture resistance and long tool life.

Among the cutting tools of Experimental Examples 1 to 12, Experimental Examples 1 to 11 satisfy at least one of the requirements regarding the ratio of the area occupied by the grain boundary phase described above and the requirements regarding the morphology of the silicon nitride or sialon particles described above. The amount of damage was smaller than in Experimental Example 12, which did not satisfy either of these two requirements. From this result, it was found that the cutting tools of Experimental Examples 1 to 11 had even better fracture resistance than Experimental Example 12.

Among the cutting tools of Experimental Examples 1 to 11, Experimental Examples 1 to 9 that satisfy both the above-mentioned requirements regarding the area ratio occupied by the grain boundary phase and the above-mentioned requirements regarding the morphology of silicon nitride or sialon particles are as follows. There was a tendency for the amount of damage to be smaller than in Experimental Examples 10 and 11, which did not satisfy only one of the two requirements. This result suggested that the cutting tools of Experimental Examples 1 to 9 had even better fracture resistance than Experimental Examples 10 and 11.

Among the cutting tools of Experimental Examples 1 to 9, Experimental Examples 1 to 8, which satisfied the requirements regarding the halo pattern in the surface area described above, had a greater amount of damage than Experimental Example 9, which did not satisfy the requirements regarding the halo pattern in the surface area. There was a tendency for it to become smaller. This result suggested that the cutting tools of Experimental Examples 1 to 8 had even better wear resistance than Experimental Example 9, and thus had a longer life. Note that the reason why a halo pattern was observed in the surface area of Experimental Example 9 is presumed to be because the amount of WC contained in the TiN powder used for manufacturing was small.

The present invention is not limited to the embodiments detailed above, and various modifications and changes can be made within the scope of the claims of the present invention.

1 ... Cutting tool 2 ... Silicon nitride sintered body 3 ... Matrix phase 4 ... Hard phase 10 ... Grain boundary phase 11 ... Glass phase 12 ... Crystal phase

Claims (1)

A cutting tool made of a silicon nitride sintered body containing a matrix phase made of silicon nitride or sialon, a hard phase, and a grain boundary phase in which a glass phase and a crystal phase exist,
The silicon nitride sintered body is
Containing yttrium in an oxide equivalent of 5.0 wt% or more and 15.0 wt% or less, and containing titanium nitride as the hard phase of 5.0 wt% or more and 25.0 wt% or less,
In the X-ray diffraction peak in the silicon nitride sintered body,
In an internal region deeper than 1.0 mm from the surface of the silicon nitride sintered body, a halo pattern is exhibited in a 2θ range of 25° to 35°,
Regarding the maximum peak intensity A of the matrix phase and the maximum peak intensity B of the crystalline phase present in the grain boundary phase, which are defined as follows, the ratio of the maximum peak intensity B to the maximum peak intensity A is B/A is
In the surface area up to 0.2 mm from the surface of the silicon nitride sintered body, the following formula (1) is satisfied,
The internal region of the silicon nitride sintered body satisfies the relationship of formula (2) below,
When observing the cross section of the silicon nitride sintered body,
Among all the particles of the silicon nitride or the Sialon, the proportion of particles having a maximum diameter of 0.5 μm or less is 50% or more,
A cutting tool, wherein among the silicon nitride or sialon particles having a minimum diameter of 0.5 μm or more, the number of particles having an aspect ratio of 1.5 or more is 55% or more.

0.11≦B/A≦0.40...Formula (1)
0.00≦B/A<0.10...Formula (2)

When the matrix phase consists of a single type, the maximum peak intensity A is determined as the maximum peak intensity of that phase, and when the matrix phase consists of multiple types, the maximum peak intensity A is determined as the sum of the maximum peak intensities of each of those phases. demand.
The maximum peak intensity B is determined as the maximum peak intensity of the crystal phase existing in the grain boundary phase when it consists of a single type, and the crystal phase existing in the grain boundary phase consists of multiple types. In this case, it is calculated as the sum of the maximum peak intensities of each of those phases.

Images